NINETEEN homes have collapsed and hundreds of people have been injured after a 6.5 magnitude earthquake hit Japan's south-western island of Kyushu.

News agencies have now reported nine people are dead after the powerful quake sparked fires and left many trapped in the rubble.

Government officials said at least 12 people were injured and 19 houses collapsed in Kumamoto prefecture on Kyushu. 

Hundreds of military personnel have been dispatched to respond to the crisis.

The quake struck at 9:26pm local time in Kumamoto, central Kyushu, at a depth of 10 kilometres, the Japan Meteorological Agency reported.

There was no danger of a tsunami.

Hours later a another powerful quake measuring magnitude-6.4 hit the same region just after midnight local time on Friday.

One person was killed after being crushed by a collapsing building, and the other by a fire that broke out after the quake.

At least 400 people are being treated at local hospitals, public broadcaster NHK said.

Others are feared trapped under fallen structures.

"We will do our utmost and carry on with life-saving and rescue operations throughout the night," Prime Minister Shinzo Abe told reporters.

A fire also broke out in Mashiki, which has a population of around 34,000 people, and local television showed footage of firefighters tackling a blaze at a building.

Officials confirmed the region's nuclear facilities have not been adversely affected by the tremors. The plants remain in operation.

About 16,500 households in and around Mashiki were without electricity.

The US Geological Survey measured the first quake at 6.2, and put the second quake at 5.4 - another smaller aftershock followed.

Aftershocks were likely to continue for about a week, it said.